The flow cytometry core facility at the Simpson Memorial Institute has been in continuous operation under the direction of Dr. Robert F. Todd (5% effort) since October, 1984. This core laboratory provides flow cytometry services for members of the Multipurpose Arthritis Center (since 1987) as well as for investigators in the Schools of Medicine, Dentistry, Pharmacy, LSA, Public Health, and Engineering (53 investigators in FY 1990-91). Because of the major usage by members of the Multipurpose Arthritis Center (18 users in FY 1990-91), funds are requested to support 33% of the operating budget of the facility ($180,503 in the 1992-93 fiscal year). In return for this support, MAC members are eligible for a discounted recharge rate of $31 per hour (50% discount). Sample preparation is performed by individual investigators who then bring prepared samples to the core laboratory for analysis or cell sorting (see list of core services below) as performed by one of three fully trained flow cytometry operators. Reservations for flow cytometry time are made in advance (generally 3-7 days). The hours of laboratory operation extend from 8 a.m. to 6 p.m., Monday through Friday. Core laboratory equipment includes a Coulter EPICS C single laser flow cytometry system and a Coulter ELITE triple laser flow cytometry system. Current services provided to core users include the following (a) cellular light scatter characteristics as an assessment of cell size and cytoplasmic granularity; (b) surface density of one or more plasma membrane antigens or receptors; (c) DNA content (cell cycle analysis); (d) cytoplasmic calcium content/flux; (e) oxidative metabolism (intracellular H2O2); (f) cellular viability; (g) autofluorescence; (h) cell sorting (on the basis of surface antigen expression or DNA content for functional or biochemical analyses of purified subpopulations); (i) computer analysis of flow cytometry data (publication quality computer graphics) and data storage (including listmode); and (j) multi-parameter analysis (e.g., DNA content versus cell surface antigen expression).